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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Results
  • Discussion
  • Disclosures
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Abstract

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 °C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 °C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 °C.

Introduction

Temperature programmed reaction (TPRxn) is one of many temperature programmed methods, including desorption (TPD), oxidation (TPO), and reduction (TPR), and proceeds via exposure of a catalyst to a reactant concurrent with or followed by a steady increase in temperature.1,2,3 TPRxn is a transient technique that provides information about catalyst activity and selectivity as a function of reaction temperature.4,5,6 It is also a popular technique: a search of the keywords 'temperature programmed reaction' in the literature yields over 1,000 sources citing its use.

TPRxn experiments are typically performed in a microreactor system, equipped with a mass spectrometer (MS) for real-time analysis of the reactor effluent and correlation of performance with temperature. Reactant gases can be introduced using mass flow controllers and liquids can be introduced via a syringe pump or as vapors by bubbling inert gas through a liquid. The catalyst is often pre-treated in situ to form the desired catalytic phase for the reaction. Some systems are equipped with additional analytical equipment, beyond the typical mass spectrometer, to provide quantitative or qualitative information about the catalyst selectivity, surface species present on the catalyst, or reaction mechanism. For example, temperature programmed in situ Fourier Transform Infrared Spectroscopy (FTIR) provides information about the evolution of surface species with varying reaction temperature.7,8 The TPRxn system demonstrated in this work is equipped with a gas chromatogram (GC) in addition to the more typical MS. This GC, equipped with four parallel columns, allows for more accurate quantification of the reaction products, but is limited in analysis frequency by the time it takes the products to elute through the columns. Thus, the combination of MS and GC can be particularly useful for coupling real-time identification with accurate quantification of reactants and products.

Here, we apply the TPRxn methodology to study the deoxygenation of acetic acid on molybdenum carbide catalysts. This is an interesting and important reaction in catalyst research, as acetic acid is a useful analog for the many carboxylic acids present in biomass pyrolysis vapors.9 The high oxygen content in biomass pyrolysis vapors necessitates oxygen removal to produce hydrocarbon fuels,10,11,12 and molybdenum carbide catalysts have shown promising deoxygenation performance for many biomass pyrolysis vapor model compounds, including furfural, 1-propanol, phenolics and acetic acid.9,13,14,15,16 However, the activity and selectivity of molybdenum carbide catalysts in deoxygenation reactions is dependent on the catalyst structure and composition, the reacting species and the reaction conditions.

The data collected from TPRxn of acetic acid shows that molybdenum carbide catalysts are active for deoxygenation reactions above ca. 300 °C, and when combined with catalyst characterization information allows for quantification of the catalyst activity as a function of temperature via the calculation of acetic acid turnover rates. The TPRxn results show that deoxygenation (i.e., C-O bond-breaking) products are favored at temperatures below ca. 400 °C and decarbonylation (i.e., C-C bond-breaking) products are favored at temperatures above ca. 400 °C. Additionally, TPRxn studies illustrate the changes in the activity and selectivity of molybdenum carbide catalysts produced using various synthetic procedures (i.e., the production of different molybdenum carbide catalyst structures and compositions). Still, the value of this information and, more generally, the successful application of TPRxn experimental data toward catalyst design and process optimization is a function of the quality of the data obtained. Careful consideration and knowledge of the potential difficulties and limitations highlighted throughout the TPRxn procedure is paramount.

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Protocol

CAUTION: Consult safety data sheets (SDS) for all chemicals used prior to operation. Flammable gases may present explosion hazards if combined with air or oxygen and an ignition source. Hydrogen is an extremely flammable gas. Acids are corrosive, and in the case of skin or eye contact, are irritants and may produce burns. Acetic acid is a flammable liquid and vapor and thus may ignite and/or explode in the presence of open flames, sparks and oxidizing agents, in addition to potentially causing severe skin burns and eye damage. When not in a closed system or container, acetic acid should be handled inside of a chemical fume hood. The hazards of nanomaterial catalysts are not well-understood, thus these materials should be handled inside local exhaust enclosures (i.e., a chemical hood) to reduce exposure. Personal protective gear (safety glasses, nitrile gloves, lab coat, closed-toed shoes, long pants) should be worn while handling any of these materials.

NOTE: The quadrupole mass spectrometer (MS) used in this work is equipped with a Faraday cup detector and operates at an ionization energy of 70 eV. For quantification of all reaction products, the micro gas chromatograph (µGC) includes a total of four independent columns each equipped with a thermal conductivity detector (TCD). For column types refer to the Specific Equipment/Materials list. Clean gas filters are used on the µGC carrier gases (He, Ar) to prevent column degradation due to H2O, and to improve the performance of the thermal conductivity detectors. Briefly, µGC units are typically less expensive and have shorter sample times than conventional gas chromatograph systems, but are restricted in the compounds that can be analyzed (i.e., most effective for permanent gases, short chain hydrocarbons and low molecular weight oxygenates) and are limited to thermal conductivity detectors.

1. System Preparation

  1. Equipment Startup
    1. Verify the MS and µGC are powered on, stabilized, tuned, and the µGC is calibrated. For tuning and method development of the MS and µGC, refer to the operating manual of the analytical equipment. Detailed procedures for µGC calibration are published elsewhere17,18,19,20,21, and an overview of the specific calibration process used here is presented in the note below.
      NOTE: Compounds were identified through retention time comparison with known standards. Quantitative analysis was carried out using TCDs, which were calibrated with standards of known concentrations. Briefly, each gas standard was fed to the µGC with a two-stage regulator and the concentrations were allowed to stabilize. Once gas concentrations stabilized as evidenced by stabilization in the chromatogram peak areas, at least three samples of the calibration gas standard were taken. The process was repeated for all relevant gas standards. Response factors for each species were generated from the line of best fit of the peak areas from the triplicate calibration samples as a function of the known gas standard concentrations. The species and concentration ranges observed in the experiment, and thus needed for calibrations, are outlined in Table 1. In general, a minimum of three calibration points for each species, spanning the entire expected range, is preferable. For relatively non-volatile (i.e., low vapor pressure) species such as acetic acid, obtaining gas calibration standards with appropriate concentrations may be difficult, and thus single-point calibrations may be the only option.
    2. To prevent condensation of gas phase reactants and products in the system lines, ensure that the system lines from the reactor to the MS, and from the MS to the µGC are heated to 84 °C and 105 °C, respectively, using insulated heat tapes (Figure 1A) and a heat tape temperature controller. These temperatures are chosen based on the boiling points of the reactant and product species, manufacturers specifications for the maximum allowable temperature for gas fed to the µGC, and the need to maintain a sufficiently low MS vacuum pressure.
      NOTE: All system lines are 316/316L stainless steel unless otherwise noted. VCR and compression type fittings are used exclusively throughout the system, with one exception at the reactor thermocouple. The fittings connecting the quartz "U-tube" reactor to the system tubing are VCR; however, Ultra-Torr fittings would also be applicable under the conditions employed in this work. Such a fitting is used for the reactor thermocouple, in conjunction with a bored-through union, allowing the position of the thermocouple to be adjusted. An acetic acid compatible O-ring (perfluoroelastomer) is used for this fitting.
    3. Use a roughing pump to decrease the MS pressure below 1x10-4 Torr.
    4. Power on turbo vacuum pump for the MS and allow the vacuum pump sufficient time to reach desired vacuum pressures (<1x10-7 Torr).
    5. Fill saturator (Figure 1B) with glacial acetic acid in an appropriate ventilated fume hood.
      1. Carefully pour the acetic acid into the saturator; minimize contact between the acid and the stainless steel "cutting edge" that will be used to complete the fitting with the copper gasket.
      2. Place a copper gasket on the bottom half of the saturator unit, and align the top half of the saturator in place.
      3. Insert the bolts through the flange holes, and hand-tighten into the washers. Use a wrench to tighten the bolts further, alternating bolts after each half turn to ensure a uniform seal across the copper gasket.
    6. Install saturator on TPRxn system.
      NOTE: When installing the saturator, ensure the orientation of the saturator is correct. Helium should flow through the stainless steel tubing into the liquid acetic acid, with the vapors exiting the saturator through the headspace. Improper installation could result in liquid acetic acid entering the system lines.
  2. Reactor Loading
    1. Remove a clean, dry, quartz "U-tube" reactor (Figure 2) from a storage/drying oven (nominally kept at 110-150 °C).
    2. Once the reactor has cooled to room temperature, load a small amount of quartz wool into the reactor. Use the minimum amount of quartz wool needed to support the catalyst bed.
    3. Using a clean, stiff, metal wire packing rod (e.g., 3/32" OD, 316/316L stainless steel), gently push the wool down the quartz tube to the end of the straight section of the tube.
    4. Weigh 50 mg catalyst, and mix with 200 mg quartz chips to prevent channeling and to ensure consistent temperature through the catalyst bed. Prior to use, sieve quartz chips to a particle size similar (i.e., 180-300 µm) to that of the catalyst (i.e., 150-250 µm) to limit inhomogeneity of the physical mixture.
      NOTE: Sieving the quartz chips to a smaller particle size may result in a larger pressure drop across the catalyst bed.
    5. Using weigh paper and a clean funnel, pour catalyst/quartz chip mixture into the reactor, such that the catalyst bed sits on top of the quartz wool support.
    6. Gently push a second small piece of quartz wool on top of the catalyst bed, securing the catalyst bed in place.
  3. Reactor Installation
    1. Clean reactor thermocouple with acetone to remove any residue from previous experiment.
    2. Install the reactor by first connecting and tightening the fitting on the upstream side of the catalyst bed (i.e., the straight section of the quartz reactor tube).
    3. Connect and tighten the fitting on the downstream side of the catalyst bed. The short section of flexible stainless steel tubing used for this fitting in the system demonstrated here mitigates potential breaks in the delicate "U-tube" reactors during reactor installation and removal.
    4. Adjust the reactor thermocouple position by pushing the thermocouple through a bored-through fitting so that the tip of the thermocouple sits on the top edge of the catalyst bed. The thermocouple should be pushed through the quartz wool located on top of the catalyst bed.
      NOTE: A perfluoroelastomer (FFKM) O-ring is compatible with reactants and products present in this experiment and is therefore recommended for sealing the fitting.
    5. Carefully raise the furnace (Figure 1C) to the highest level allowed by the "U-tube" reactor, such that the top edge of the furnace does not touch the reactor. Do not allow the bottom of the reactor to contact the bottom of the furnace.
    6. Wrap the exposed sections of the "U-tube" reactor above the furnace with insulation.

2. Reactor Startup

  1. Inert Purge
    NOTE: The reactor system and analytical equipment must vent to a safe location such as a fume hood so that people and other lab equipment are not exposed to harmful gases and vapors. Prior to starting flow of any gas, the respective compressed gas cylinder and two-stage regulator delivery valves should be opened. If needed, the regulator delivery pressure should be adjusted to the inlet pressure at which the associated mass flow controller (MFC) was calibrated. The delivery pressure from the MFCs should not exceed 140 kPa, a limit defined by the maximum allowable pressure at the inlet of the µGC.
    1. Open the shut-off valve between the ultra-high purity (UHP) He MFC and the reactor (this valve is present to prevent backflow to the He MFC), and ensure the three-way valve is routing gas from the reactor to the local exhaust ventilation line (Figure 3).
      NOTE: Unless otherwise specified, all pressures are given relative to local barometric pressure (gauge pressures). The addition of water traps to each gas feed line is recommended to remove any trace water from the gas.
    2. Flow UHP He gas at 40 standard cubic centimeters per minute (sccm) through the calibrated MFC. This flow rate has been empirically determined to effectively purge the system of air and residual gases within a reasonable time frame (ca. 45-60 min).
      NOTE: Valves have been placed immediately downstream of the MFCs to prevent backflow of residual acetic acid vapors, which may result in damage to the MFCs. When starting gas flow, it is important to start flow through the MFCs immediately after opening these system line valves.
    3. Verify that the system pressure does not rise to more than 7 kPa.
      NOTE: A higher system pressure may indicate that a valve is closed or that the pressure drop through the catalyst bed is higher than acceptable. If the latter, increasing the amount of quartz chips mixed with the catalyst may decrease the pressure drop across the catalyst bed.
    4. Using the computer software associated with the MS, start the online MS. Set the MS to scan from mass-to-charge (m/z) ratios of 0 to 100.
      NOTE: Using a scan mode is preferred to using a selective ion monitoring (SIM) mode as it allows for detection of unknown products. The scan range is chosen based on limitations of the MS and a scan over the range of 0-100 (m/z) is typically sufficient for analysis of the major acetic acid reaction products. If equipment allows a larger range, scanning up to 102 would be desirable to include detection of any acetic anhydride produced.
    5. Open the MS gas sampling orifice valve to allow the vacuum of the MS system to draw gas through the 1 µm orifice.
      NOTE: A 2 µm filter incorporated into a VCR gasket is installed just upstream of the 1 µm orifice to limit plugging of the 1 µm orifice.
    6. Purge air from the acetic acid saturator with UHP He by opening the inlet and outlet saturator valves, and subsequently closing the saturator-bypass valve. Continuous bubbling through the liquid acetic acid indicates that the system line valves are in the correct position and that the saturator was installed with the correct flow orientation. Allow the saturator to purge while monitoring the MS signal until N2 and O2 (m/z = 28 and 32, respectively) are no longer present.
      NOTE: Step 2.1.6 may be skipped if it has been performed in previous experiments.
    7. Stop the saturator purge by opening the saturator bypass valve and closing the saturator inlet and outlet valves.
    8. Continue purging the system with UHP He until all m/z signals except He (m/z = 4) are no longer present (may require 45-60 min depending on system volume).
      NOTE: System may remain under UHP He flow until ready to begin subsequent steps.

3. Catalyst Pretreatment

  1. In-Situ Hydrogen Pretreatment
    NOTE: At this point, the catalyst exists as molybdenum carbide and was synthesized ex-situ via methods published elsewhere.9,22 The in-situ hydrogen pretreatment step is included to remove surface oxygen (often resulting from the oxygen passivation following synthesis), and/or to remove organic ligands that may be present on the catalyst surface as a result of synthesis.
    1. Continue UHP He flow at 40 sccm.
    2. Open the H2 tank cylinder valve. Adjust the two-stage regulator delivery pressure if needed, and open the regulator needle valve (see NOTE in 2.1.1).
    3. Begin H2 flow by opening the H2 system line shut-off valve just downstream of the H2 MFC and setting the MFC to flow at 1.3 sccm. Adjust UHP He flow to 36 sccm.
      NOTE: A 3.5% H2/He gas mix is chosen to keep the H2/He composition below the lower explosive limit of hydrogen (4%). The flow rate of 37.3 sccm is chosen to achieve the desired mix composition given the flow range limitations of the MFCs on our system, to ensure a steady supply of H2 during the catalyst pre-treatment, and to maintain a system pressure below 140 kPa.
    4. Allow the gas phase concentrations of H2 and He to stabilize (30-45 min) by monitoring the MS signals m/z = 4 and 2 for He and H2, respectively.
    5. Enter the temperature program into the furnace controller. A typical temperature program is as follows: ramp from room temperature to 400 °C at 5 °C/min, holding at 400 °C for 2 h.
      NOTE: The reduction temperature and holding time are often material dependent and empirically determined. Here, these values were determined based on previous temperature programmed reduction studies of molybdenum carbide catalysts which indicate when O2 removal by H2 as H2O is complete. As an example, for bulk orthorhombic β-Mo2C, the O2 removal was complete following 2 h at 400 °C. The ramp rate of 5 °C/min is sufficiently slow to ensure the pre-treatment is not destructive to the catalyst and sufficiently fast to complete in a reasonable time period.
    6. Begin the temperature program.
    7. When the program ends, allow the reactor to cool to ambient temperature in flowing 3.5% H2/He.

4. Acetic Acid Temperature Programmed Reaction (TPRxn)

  1. Starting an Experiment
    1. Continue flowing UHP He and H2 at flowrates of 36 and 1.3 sccm, respectively.
    2. Begin the flow of acetic acid vapors through the reactor by opening the inlet and outlet saturator valves, and subsequently closing the saturator-bypass valve.
    3. Route gas flow to the µGC by switching the three-way valve downstream of the reactor from its current position (sending gas from the reactor to the local exhaust vent) to the µGC position.
      NOTE: System pressure should begin to increase. This pressure increase is due to the pressure drop through the 1/16" tubing used in the µGC unit and should not be allowed to exceed 140 kPa (this limitation is based on the maximum allowable pressure at the inlet of the µGC).
    4. Allow the system pressure and gas phase concentration of acetic acid to stabilize (requires 60-90 min depending on system volume).
      NOTE: Acetic acid concentration may be tracked on the MS by visualizing the real-time data from m/z = 43 and 60. System pressure typically stabilizes at approximately 130 kPa.
    5. Program the furnace temperature controller to ramp from room temperature to 600 °C at 10 °C/min.
      NOTE: The ramp rate of 10 °C/min is sufficiently slow to obtain well-resolved data as a function of temperature and to avoid any destruction to the catalyst, but sufficiently fast to complete the experiment within a reasonable period, and without substantial catalyst deactivation.
    6. Begin collecting µGC samples as frequently as possible.
      NOTE: The µGC method used here allows for sampling once every 5.5 min. The MS data should include temperature vs. time data and the µGC data should include synchronized time stamps such that both the MS and µGC data can be correlated with temperature.
    7. Begin the temperature program immediately after starting the µGC samples.
  2. Stopping an Experiment
    1. When the temperature program has completed, stop the µGC sequence.
    2. Using the computer software associated with the MS, turn the MS off.
      NOTE: Leave the MS turbo pump 'on' if the MS is to be used in subsequent experiments.
    3. Close the 1 µm MS orifice valve.
    4. Load a µGC method that sets the column temperatures to their maximum allowable limit, as recommended by the manufacturer.
      NOTE: Carrier gases to the µGC must remain on. This 'bakeout' method is recommended by the manufacturer to remove (clean) oxygen, water, and high-boiling compounds from the µGC columns.
    5. Shut off hydrogen flow by setting the H2 MFC to 0 sccm and closing the H2 shut-off valve.
    6. Allow the reactor to cool to ambient temperature while purging the system with flowing UHP He at 40 sccm.
    7. When cool, turn off UHP He flow, and allow the system to reach ambient pressure.
    8. Once at ambient pressure, route gas to the local exhaust vent using the three-way valve.

5. Reactor Unloading

  1. Uninstalling a Reactor
    1. Stop UHP He flow by setting the He MFC to 0 sccm. Close the UHP He line shut-off valve located immediately downstream of the He MFC.
    2. Loosen the Ultra-Torr thermocouple fitting and pull the thermocouple up and away from the catalyst bed to facilitate reactor removal.
    3. Uninstall the reactor by first disconnecting the fitting on the downstream side of the reactor (i.e., the fitting connected to the flexible stainless steel tubing).
    4. Disconnect the fitting on the upstream side of the reactor.
    5. Remove the reactor from the system and transport to a chemical fume hood.
  2. Reactor Cleaning
    1. Working in a chemical fume hood, use a clean, corrosive resistant wire (e.g., 24 gauge nichrome wire) to remove the piece of quartz wool on the top of the catalyst bed.
    2. Pour the used catalyst into a sample vial to keep in case post-reaction characterization is desired at a later time.
    3. As in 5.2.1, use the wire to remove the remaining piece of quartz wool.
    4. Clean the inside of the reactor with acetone.
      NOTE: A pipe cleaner may be used in conjunction with acetone to scrub the inside of the reactor if any residual carbon is present.
    5. Store the reactor in an oven at 110 °C to remove any residual water. If an oven is not available, the reactor can be blown dry using a compressed air line in a chemical fume hood and stored in a desiccator.

6. Data Analysis

  1. MS Deconvolution
    NOTE: The method for MS deconvolution is briefly outlined here. Refer to recently published literature for a complete summary of the deconvolution of acetic acid TPRxn MS data.9,23
    1. Using the MS software, download individual m/z ratio data as a function of reaction temperature.
    2. Adapting a method used by Zhang, et al.24, correct for overlapping MS signals using mass fragmentation patterns for individual species (see discussion section below).
    3. Correct the deconvoluted MS data similar to the method described by Ko, et al.,25, for relative differences in ionization efficiency, quadrupole transmission and electron multiplier gain.
    4. Use the normalized and corrected data to gain semi-quantitative information regarding catalyst performance.
  2. µGC Data Integration and Analysis
    1. Using the µGC software, integrate chromatogram peaks.
    2. Using the response factors generated from the µGC calibration discussed in section 1.1.1, transform peak area counts into molar composition data for each species observed.
    3. Refer to recent literature for a detailed explanation of the µGC data analysis procedure and the quantitative information it can provide.22

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Results

The online MS provides the capability to analyze the gas composition at the reactor outlet in real-time. The online MS is not coupled with any device to separate products prior to analysis, and thus species identification is challenging when differentiating between compounds with overlapping mass fragmentation patterns. As shown in Table 2, many of the common products from acetic acid TPRxn experiments are characterized by multiple common m/z signals. Deconvolution of the...

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Discussion

The TPRxn method is a powerful tool for screening of catalytic materials, providing information about the activity and selectivity of a catalyst as a function of reaction temperature. Other temperature-programmed methods such as TPD, TPO and TPR can provide information on the adsorption strength of reactants, number of adsorption sites, and appropriate catalyst pre-treatment procedures, but do not provide direct catalytic performance data. It is important to note that the TPRxn method detailed in this work does not measu...

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Disclosures

The authors have nothing to disclose.

Acknowledgements

This work was supported by the Department of Energy Bioenergy Technologies Office under Contract no. DE-AC36-08-GO28308. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

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Materials

NameCompanyCatalog NumberComments
glacial acetic acidCole-ParmerEW-88401-62alternate supplier acceptable if ACS purity grade. See caution statement in protocol for safety information
UHP HeAirgasHE R300SSalternate supplier acceptable if >99.99% purity
UHP ArArigasAR R200alternate supplier acceptable if >99.99% purity
acetoneVWR InternationalBDH1101-4LPalternate supplier acceptable if >99.5% purity
quartz chipsPowder Technology Inc.Crushed Quartzsieved 180-300 µm, calcined in air at 500 °C overnight
mass spectrometer - turbo vacuum pumpPfeiffer VacuumTSU 071mass spectrometer is controlled with LabVIEW 2010 software package (National Instruments)
mass spectrometer - turbo vacuum pumpStanford Research SystemsRGA100
micro gas chromatographAgilentCP740388490 Micro GC; 4-channel system
Channel 1: 494001360 Molseive 10m, heated backflush
Channel 2: 494001460 PPU 10m, heated backflush
Channel 3: 490040 AL2O3/KCL 10+0.2m, heated backflush SPECIAL
Channel 4: 492005750 5CB 15m, heated
GC softwareAglientOpenLAB CDS EZChrom Edition
clean gas filtersAgilentCP17974for use on GC carrier gases (He, Ar)
quartz "U-tube" reactorn/ahand blown glass, custom built to order
bubblern/acustom built to order
ceramic furnaceWatlowdiscontinuedSimilar furnace part #: VC401J12A-B000R
heat tape controllern/acustom built with Watlow EZ-zone parts
heat tapeOmegaFGH051-060alternate supplier for extreme temperature heat tape acceptable
heat tape insulationJEGS710-80809alternate supplier acceptable
thermocoupleOmegae.g., KMQSS-062U-18K-type thermocouples; alternate sizes may be required
thermocouple O-ringSwagelokVT-7-OR-001-1/2perfluoroelastomer(fluorocarbon FKM) O-ring
2 µm solids filter, VCR gasketSwagelokSS-4-VCR-2-2M
1 µm orifice, VCR gasketLenox LaserSS-4-VCR-2for mass spectrometer orifice
316/316L stainless steel tubing and fittingsSwagelokVariesSee Swagelok 'VCR Metal Gasket Face Seal Fittings' and 'Stainless Steel Seamless Tubing and Tube Support Systems' catalogs for more information
316/316L stainless steel tubing and fittingsSwagelokVariesSee Swagelok 'Integral-Bonnet Needle Valves', 'Bellows-Sealed Valves' and 'One-Piece Instrumentation Ball Valves' catalogs for more information

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